Process of sweetening petroleum distillates



May 25,1942. MQKjJONES'ETAL 2,320,271

PROCESS OF SWEETENING PETROLEUM DISTILLATES.

Filed 0G11. A29, 1941 wn rez: INLET /2 VEN-r SUL'FIDE. Q SET-)7.52

/NT'ERNEDIATE TANK / l WATER Ov7-g7- Patented May 25, 1943 PROCESS 0F SWEETENING PETROLEUM DISTILLATES i Minor C. K. Jones, Bound Brook, and Richard C.

Brandon, Elizabeth, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application October 29, 1941 Serial No. 416,962 s claims. (01.19643),

This invention relates to the art of sweetening petroleum distillates involving the dispersion of a metal sulde, e. gf., lead sulde, in the sweetened petroleum distillate, and has the object of facilitating the separation and recovery of the metal sulfide from the sweetened distillate.

Sweetening treatments are used to improve odor,` correct corrosion,- and eliminate sulfurcontaining compounds which have deleterious effects on the stability and combustion qualities of hydrocarbon oils. Mercaptans are the sulfurcontaining impurities which are largely responsible for the need of sweetening petroleum distillates, and in a number of sweetening' treatments, are reacted with salts of metals, such as lead, copper, zinc, magnesium, sodium, calcium, and the like, to yield metal suliides which tend to remain suspended in the oils. The `present invention is applicable to these treatments, particularly in so far as they form suspensions of metal sulfides which are not readily hydrolyzed and removed bywashing with water.

The most common sweetening process lsknown as the doctor` treatment. -This treatment, and modifications thereof, involve the formation or use of metal sulfides *which tend to remain suspended in the sweetened oil to some extent, thus requiring a water washing step and recovery of the metal suliides from the wash Water.

The doctor treatment consists in agitating a sour distillate (one containing mercaptans), with a, controlled amount of sulfur and an alkaline sodium plumbite solution. The reaction results in the conversion of mercaptans toless objectionable organic disulfldes Aand formation of lead sulfide. Most of the lead sulfide formed is separated by settling from the treated oil but some remains suspended or entrained in the sweetened oil. `Accordingly, lthis oil is washed with water to remove the remaining suspended leadsulfide.

With the procedure of washing hitherto used, it has been impractical to satisfactorily remove the suspended lead sulde from the sweetened oil tothe extent desired due to limitationsof time, apparatus, and the amount of wash water; and as a result, substantial amounts of lead sulfide left in the oil annoyingly have settled out in storage tanks. Use of wash water in' extra large quantities makes recovery of the metal sulde more diiiicult, because a portion of the metal .sulfide tends to remain in the water phase, and results in a greater loss of lead, excessive consumption of water and power, greater loss in hydrocarbon product, and troubles from pollution of streams or rivers' by the waste water. Consequently, it is very important to improve the water washing procedure so as to obtain a more rapid separation of the lead sulfide with a restricted amount of water and apparatus.

In accordance with the present invention, certain organic substances, particularly polysaccharides, which characteristically form muoilaginous colloids with water, are used to effectively expedite the separation of lead sulde, up to the last traces thereof, from a sweetenedhydrocarbon oil in the washing step, and thereby leave a clear sweetened product. i

For example, by admixing a small amount, e. g., about 0.25% by weight of starch or dextrin (starch gum) with a certain amount of wash water, the time for separation of the lead sulde from a sweetened naphtha was shortened to about one minute and less, whereas by omitting these agents from about 25 to 50 times as much time was required for the separation.

The amount of these agents required for making a considerable increase in the separation rate' is very small, being of the order of from about 0.05% to about 1% by weight of the water, and more preferably, in the range of 0.1% to 0.5%; therefore they are used in an extremely small proportion with respect to the hydrocarbon liquid treated, since only about 5% to about 30% by volume of water is used on the basis of hydrocarbon liquid treated.

The agents found to be useful in the manner described for accelerating the washing procedure vary to some extent in composition and in certain properties; hence, there is some variation in the convenience of their employment. However, they A belong to recognized classes of related organic compounds. As a principal classification, these compounds are polysaccharides which are capable of being hydrolyzed to simple (mono-saccharide) sugars and are represented by the general formula (CHioOs) n, wherein n is a large number, greater than 3.

Dextrin, which behaves very satisfactorily, is a polysaccharide formed by partial hydrolysis of starch,- ,and it, in turn, yields glucose on hydrolysis with acids. It is soluble in water. For example, using 10% by volume of wash water containing 0.25% by weight of dextrin for Washing a sweetened naphtha containing a small amount of suspended lead sulfide, following sweetening and settling, the last traces of lead sulfide were separated out bythis `washing in about 30 seconds, and in less than 1 minute.

' Starch was used with good results. The starch may be water-soluble, or it may be insoluble in cold water but readily swelled on heating. Starches in general were found to be effective and conveniently applied.

Agar-agar, which is another type of polysaccharide, was found effective when admixed with heated water. It isinsoluble in cold water, but slowly swells and becomes soluble in hot water. By slightly acidifying the wash water, the agaragar may be dispersed therein more readily at moderate temperatures.

In addition to the typical polysaccharides melitioned, there are numerous others whichvmay be used but which are ordinarily llessL available and more expensive, e. g., guin arabic', inulin etc.

The preferred types of agents to be used for aiding the separation of the suspended metal sulfide in the washing step are those that are stable under the treating conditions andl` are readily dispersed homogeneously or colloidally in the wash water before o'r during its contact with the hydrocarbon liquid.

For the purpose of illustration, a preferred embdirnent of the invention will be described with reference to a doctor sweetening process and with reference to the' accompanying drawing.

In the drawing' isshown a' o'w diagram fory a continuous doctor sweetenirlg plant in which the present process may be applied.

Referring to' the" drawing, a-sour petroleum dis'- tillate to be sweetened is: charged by inlet line I into' mixer 2, equipped internally with orince mixing plates 3. In this mixer the sour oil dis; tillate is intermiXed and agitated with the doctor treating solution (sodium plumbite) entering the mixer from line 4'. Generally,v the sour oil entering the mixer contains the desired am'ount of added free' sulfur.

From the mixer 2,- the reaction mixture ispassed by line 5 to thel lead sulfide settler Ici, in which the lead sulfide vsettled to the bottom is withdrawn together with spent' treating agent-by line 'I for regenerationand further use.

sweetened oil from which most of the lead sulfide has been settled, is withdrawn from settler 6 by line IIl to the water washing tower II equipped with wash water inlet I2, pressure control outlet I3, spent wash water drain I4, andiinished oil product outlet I5.

The spent wash water is delivered by line I4 to i a water settling tank I5, equipped with a bottom drain IG for removal of water, which may be recycled to' wash tower II, an intermediate take-od line I'I for removal of water containing a concentrated suspension of metal sulde, and

The use of the settling'agents herein describedl may b practiced in various modiiications of theA doctor treatment. They may be .used where swe'etening is conducted in a batch system. They may be employed in obtaining complete separation of suspended metal sulfide" when lead sulfide is used by itself as a sweetening agent or with some other metal compound.

It is to be noted that agents which were found satisfactorily effective are 'substantially insoluble in the oil but have a certain amount of ainity for water. In general, they are neutral and nonionic. Hence, they are beneficially used in obtaining a neutral n'ished distillate satisfactorily free of the agent and metal salts.

In general, the washing treatment is carried outnear atmospheric pressure ranging up to about 30 lbs/sq. in. gauge and at temperatures varying from about 30 F. to 120 F.

The preferred agents have been used to obtain a rapidly completed separation of metal sulfide with about half the amount of wash water ordinarily used'.

A further advantage with the separation agents of the polysaccharide type is that they may be used to electively concentrate the metal sulfide' in a relatively small aqueousv layer between the substantially suliide-free upper oil layer and v lower body of water in a water settler so that recovery of the' concentrated metal sulde is expedited,l the used wash water is in good condition and easily recycled, and a good recovery of oil from the spent wash water is obtained.

It is` not intended that the invention be limited to the specific examples which have' been given for the purpose of illustration', but it is intended that all modifications coming within the spirit of the invention be included' in the scope' thereof as defined in the appended claims.

We claim:

l. In a process oi sweetening hydrocarbon d-istillate oils containing mercaptansA involving the dispersion of metal suliides in the sweetened dis'- tillate product, the step comprising separating said m'etal sulndesf from the oilsv with the aid of an aqueous dispersion of a small amount of a polysaccharide.

2. In a process of sweetening a sour petroleum distillate by a doctor solution of alkaline sodium plumbite,v` the step of removing the last traces of .f lead sulfide from the sweetened oil which comprises washng the sweetened oil with water containing a small amount of starch dispersed therein.

3. In a process of sweetening a sour petroleum distillate by a doctor solution of alkaline sodium plumbite, the step of removing final traces of lead sulfide from the sweetened oil which comprises washing the sweetened oil with water containing a small amount of dextrin.

4.- In a kprocess o'f sweetening a sour petroleum ii'rstillate by a doctor solution of alkaline sodium plumbite, the'ste'p of removing nal traces of lead sulfide from the sweetened oil which comprises was'hing the' sweetened oil with water containing a small amount of agar-agar dispersed therein.

5. In a process of sweetening a petroleum distillate containing mercaptans with a compound of ametal which forms a suspension of metal sulfide diicult to remove from the distillate by water washing, the improvement which comprises incorporating into water used the sweetening distillate about 0.05% to 1% of a polysaccharide based on the weight of the water.

6. The steps of washing out and recovering nal traces of suspended lead sulde from a doctor sweetened petroleum distillate, which comprises washing said sweetened distillate with from about 5% to 30% by volume of water containing about 0.05-% to about 1% by weight of a.

polysaccharide which is capable of being hydrolyzed to glucose, separating spent wash Water from the distillate, said spent wash water containing lead sulfide and entrained hydrocarbons,

I settling said spent wash Water in a settling zone,

ing nal traces of the suspended lead sulfide by washing the sweetened distillate with water containing about 0.1% to 0.5% by weight of dextrin. 8. In a vprocess of Washing a sweetened naphtha distillate containing a small amount of suspended lead sulde to remove nal traces of the lead sulde from the distillate, the improvement which comprises contacting said distillate with about 10% by volume of water containing about 0.25% by weight of dextrin, and separating from said distillate the Wash water containing the removed last traces of lead sulde within a period of about 30 seconds.

MINOR C. K. JONES. RICHARD C. BRANDON. 

